1. Field of the Invention
The present invention relates to a metal working lubricating oil having improved lubrication properties due to the addition of certain esters of trimellitic acid to said oil.
2. Description of Related Art
The use of esters in lubricating oils is known. For example, U.S. Pat. No. 2,134,736 discloses that esters of polybasic carboxylic acids, particularly dibasic carboxylic acids, when admixed with hydrocarbon oils, are of special utility in extreme pressure lubrication applications; e.g. gear and bearing oils, metal cutting and boring oils, etc. As another example, U.S. Pat. No. 3,769,215 discloses ester lubricant compositions in which the esters are derived from polyoxyalkaline glycols with dibasic acid mixture consisting of dimer acids and shortchained dibasic acids. In yet another example, U.S. Pat. No. 4,178,260 discloses ester based metalworking lubricants in which preferred lubricants comprise a mixture of (i) tetraester of pentaerythritol and a C.sub.6 -C.sub.20 aliphatic monocarboxylic acid, and (ii) orthophosphoric acid. Finally, U.S. Pat. Nos. 4,618,441 and 4,655,947 disclose a lubricant composition comprising a mineral oil and an alkoxyalkyl ester.
However, none of the foregoing references mention a lubricating oil having improved lubricity due to the presence of tri-2-ethylhexyl-trimellitate, tri-normal-octyl-trimellitate or mixtures thereof in said oil.